Comparison of different methods of initiating lung inflammation and the sex-specific effects on inflammatory parameters.

Sex as a biological variable is an essential element of preclinical research. Sex-specific differences in lung volume, alveolar number, body weight, and the relationship between lung and body weight result in important questions about generating equivalent injuries in males and females so that comparisons in their responses can be assessed. Few studies compare stimulus dosing methods for murine lung models investigating immune responses. To examine sex-specific effects, we explored several dosing techniques for three stimuli, LPS, Streptococcus pneumoniae , and influenza A, on survival, injury parameters in bronchoalveolar lavage (BAL), and immune cell numbers in single-cell lung suspensions after injury. These data demonstrate that body weight-based dosing produced fewer differences between sexes when compared with injury initiated with inocula containing the same number of organisms. Comparison of the lung and body weights showed that females had a greater lung-to-body weight ratio than males. However, in LPS-induced injury, adjusting the dose for sex differences in this ratio in addition to body weight provided no new information about sex differences compared with dosing by body weight alone, most likely due to the variability in measures of the immune response. Studies evaluating BAL volumes revealed that smaller but more lavages resulted in greater returns and lower protein concentrations, particularly in the smaller female lungs. Thus, designing dosing and measurement methods that generate equivalent injuries facilitates comparison of immune responses between sexes. Continued development of methods for both induction and evaluation of injury will likely facilitate identification of sex differences in immune responses.